Java-Gaming.org Hi !
Featured games (90)
games approved by the League of Dukes
Games in Showcase (731)
Games in Android Showcase (217)
games submitted by our members
Games in WIP (799)
games currently in development
News: Read the Java Gaming Resources, or peek at the official Java tutorials
 
    Home     Help   Search   Login   Register   
Pages: [1]
  ignore  |  Print  
  Fast Math: sin/cos lookup tables  (Read 7621 times)
0 Members and 1 Guest are viewing this topic.
Offline Riven
Administrator

« JGO Overlord »


Medals: 1284
Projects: 4
Exp: 16 years


Hand over your head.


« Posted 2011-05-09 20:27:55 »

Math.sin() is slow. Using a lookup table for sin/cos is roughly 50x faster. The loss of accuracy is minimal, maximum error is roughly 0,001. You can probably get away with it.

1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
31  
32  
33  
34  
35  
36  
37  
38  
39  
40  
41  
42  
43  
44  
45  
46  
47  
48  
49  
50  
51  
52  
53  
54  
55  
56  
   public static final float sin(float rad)
   {
      return sin[(int) (rad * radToIndex) & SIN_MASK];
   }

   public static final float cos(float rad)
   {
      return cos[(int) (rad * radToIndex) & SIN_MASK];
   }

   public static final float sinDeg(float deg)
   {
      return sin[(int) (deg * degToIndex) & SIN_MASK];
   }

   public static final float cosDeg(float deg)
   {
      return cos[(int) (deg * degToIndex) & SIN_MASK];
   }

   private static final float   RAD,DEG;
   private static final int     SIN_BITS,SIN_MASK,SIN_COUNT;
   private static final float   radFull,radToIndex;
   private static final float   degFull,degToIndex;
   private static final float[] sin, cos;

   static
   {
      RAD = (float) Math.PI / 180.0f;
      DEG = 180.0f / (float) Math.PI;

      SIN_BITS  = 12;
      SIN_MASK  = ~(-1 << SIN_BITS);
      SIN_COUNT = SIN_MASK + 1;

      radFull    = (float) (Math.PI * 2.0);
      degFull    = (float) (360.0);
      radToIndex = SIN_COUNT / radFull;
      degToIndex = SIN_COUNT / degFull;

      sin = new float[SIN_COUNT];
      cos = new float[SIN_COUNT];

      for (int i = 0; i < SIN_COUNT; i++)
      {
         sin[i] = (float) Math.sin((i + 0.5f) / SIN_COUNT * radFull);
         cos[i] = (float) Math.cos((i + 0.5f) / SIN_COUNT * radFull);
      }

      // Four cardinal directions (credits: Nate)
      for (int i = 0; i < 360; i += 90)
      {
         sin[(int)(i * degToIndex) & SIN_MASK] = (float)Math.sin(i * Math.PI / 180.0);
         cos[(int)(i * degToIndex) & SIN_MASK] = (float)Math.cos(i * Math.PI / 180.0);
      }
   }

Hi, appreciate more people! Σ ♥ = ¾
Learn how to award medals... and work your way up the social rankings!
Offline Nate

« JGO Bitwise Duke »


Medals: 167
Projects: 4
Exp: 14 years


Esoteric Software


« Reply #1 - Posted 2011-05-10 04:25:55 »

Thanks Riven, I used code based on this in libgdx. I found in practice that it is important to have correct values for the 4 cardinal directions:
http://code.google.com/p/libgdx/source/browse/trunk/gdx/src/com/badlogic/gdx/math/MathUtils.java#43

Pages: [1]
  ignore  |  Print  
 
 
You cannot reply to this message, because it is very, very old.

 
Archive (339 views)
2017-04-27 17:45:51

buddyBro (537 views)
2017-04-05 03:38:00

CopyableCougar4 (980 views)
2017-03-24 15:39:42

theagentd (1018 views)
2017-03-24 15:32:08

Rule (994 views)
2017-03-19 12:43:22

Rule (976 views)
2017-03-19 12:42:17

Rule (974 views)
2017-03-19 12:36:21

theagentd (1073 views)
2017-03-16 05:07:07

theagentd (995 views)
2017-03-15 22:37:06

theagentd (770 views)
2017-03-15 22:32:18
List of Learning Resources
by elect
2017-03-13 14:05:44

List of Learning Resources
by elect
2017-03-13 14:04:45

SF/X Libraries
by philfrei
2017-03-02 08:45:19

SF/X Libraries
by philfrei
2017-03-02 08:44:05

SF/X Libraries
by SkyAphid
2017-03-02 06:38:56

SF/X Libraries
by SkyAphid
2017-03-02 06:38:32

SF/X Libraries
by SkyAphid
2017-03-02 06:38:05

SF/X Libraries
by SkyAphid
2017-03-02 06:37:51
java-gaming.org is not responsible for the content posted by its members, including references to external websites, and other references that may or may not have a relation with our primarily gaming and game production oriented community. inquiries and complaints can be sent via email to the info‑account of the company managing the website of java‑gaming.org
Powered by MySQL Powered by PHP Powered by SMF 1.1.18 | SMF © 2013, Simple Machines | Managed by Enhanced Four Valid XHTML 1.0! Valid CSS!